Filament specific Z offset  

RE: Filament specific Z offset

This can technically be done by adding this code to the your custom gcode field

G1 Z0.2 F500 ; Go to the level of 0.2 mm + your paper thickness
G92 Z0       ; This redefines the zero Z level

But this really should be something built in. Beyond various brands, various materials need offsets. You wouldn't want to print PETG at the same height as PLA.

RE: Filament specific Z offset

@ericlmccormick

I saw that same example somewhere in researching the proper G-code to insert in the Filament section. It seems like a G1 would not affect the offset for the entire print. Am I wrong? Either way, in the example, is the value supposed to be the correction (+ = +) or current position for the printer to correct from (+ = -)?

RE: Filament specific Z offset

@goodygizmos

The G1 command tells the nozzle to move up (+ = +) and then the G92 resets that new position as the new home. If you do baby stepping to figure out what height you need, just put that number in and the next time you run your file, you should be all set. 

Before switching to a Duet board, I used this type of code in my start gcode to fix my X, Y and Z offsets as it was a pain to fix it in firmware on the cheap Zonestar board.

RE: Filament specific Z offset

Posted by: @ericlmccormick

This can technically be done by adding this code to the your custom gcode field

G1 Z0.2 F500 ; Go to the level of 0.2 mm + your paper thickness
G92 Z0       ; This redefines the zero Z level

But this really should be something built in. Beyond various brands, various materials need offsets. You wouldn't want to print PETG at the same height as PLA.

 

What is considered the ground level (0 mm) ?

Is that the point where the nozzle actually touches the bed, or is it the point where we did the Live Z adjust configuration step ?

I am trying to determine what value to use in that G1 command. I've been mainly printing PETG, but now I have ABS and I would like to have it just a notch lower (more squish) than the PETG.

Also, what does the F parameter mean in the G1 command ?

RE: Filament specific Z offset

0mm is where the nozzle touches the bed but applies no pressure. 

Angus at Makers Muse did a good video about using a feeler gauge to get the correct setting.

In G1, F is the max  speed of the movement.

https://marlinfw.org/docs/gcode/G000-G001.html

For a Mk3 or mini Zero is the point where the pinda detects the bed.  That why the 'live z' value is negative.  So a -1000 is basically moving the nozzle 1mm closer to the bed surface.
For a printer with a physical switch its the point at which the switch gets activated.

F is feed rate.  Its the speed at which the movement command is performed at.

Doing it wrong

While the bed detection will trigger and that will be your initial z=0, you need to specify your z offset. 

The z offset is the distance that your sensor picks up the bed, minus the distance the nozzle is from the bed.

You can't move the nozzle to 0 on a Prusa, just pick a level and adjust from there

Posted by: @haevaristo

 [...] What is considered the ground level (0 mm) ?

It doesn't really matter. You are doing the following:

1. Move the nozzle to a set height.
2. Telling the printer that the current height is now some other height.

Fun fact: You can't actually move the nozzle on a Mk3 to 0 with gcode. I believe it's the same on the Mini. The lowest move you can make in gcode is 0.15mm. If you attempt to move lower, you'll usually see a message on the console.

So if you do something like:

G1 Z1.2 F500 ; Go to the level of 0.2 mm + your paper thickness
G92 Z1 ; This redefines the 1mm Z level

You've told the nozzle that 1.2mm as measured from the PINDA 0 position is really 1mm. Your nozzle will be 0.2mm higher than it thinks it is.

Is that the point where the nozzle actually touches the bed, or is it the point where we did the Live Z adjust configuration step ?

Unlike many other printers, the Prusas will try to keep you from driving the nozzle into the bed. The 0 position is where the PINDA is triggered as @Neophyl notes. The firmware will then not let you go lower than 0.15mm of this position (software endstops). When you make Live-Z adjustments, you are moving this 0 position up or down slightly.

The gcode tweaks being described are not Live-Z adjustments. Such adjustments are not saved with sheet profiles. It's a hacky way of making a correction for a specific filament by changing the printer's positioning after homing.

I am trying to determine what value to use in that G1 command. I've been mainly printing PETG, but now I have ABS and I would like to have it just a notch lower (more squish) than the PETG.

Just move Z to a level, then use G92 to subtract the desired amount from that level. 

RE: Filament specific Z offset

humm... sorry but I am not following it entirely... I currently have, e.g. -0.6 on my Z live adjust. If I want the print to go to -0.9 for a specific filament.

So I do:

G1 Z0.3 F500;
G92 Z1;

?

RE: Yes, but I wouldn't bother

Posted by: @haevaristo

humm... sorry but I am not following it entirely... I currently have, e.g. -0.6 on my Z live adjust. If I want the print to go to -0.9 for a specific filament.

So I do:

G1 Z0.3 F500;
G92 Z1;

?

 

That's the theory, yes. In reality, I found this to be a total pain in the ass and don't bother. It's one of those things that sounds like a great idea but creates headaches to keep current and you still wind up watching the first layer go down just to be sure. In the end, it didn't save any time for all the annoyance of setting it up. I rarely have to make adjustments of more than +- 0.02mm for different filaments.

@bobstro

I rarely have to make adjustments of more than +- 0.02mm for different filaments

-I assume that's a typo?.. because the difference of 2/100 mm can't really be noticed.

No, not a typo!

Posted by: @bogdanh

-I assume that's a typo?.. because the difference of 2/100 mm can't really be noticed.

No, not a typo and that's my point. I've had a couple of times where a very minor adjustment helped with a bit of PETG 1st layer scraping -- presumably, it was right on the edge -- and that was sufficient. I have, after carefully calibrating my Live-Z mind you, rarely had to make any sort of adjustment to accommodate different filaments. I don't put much thought into swapping between PLA and PETG other than cleaning the hotend and nozzle. I've read of people going as high as +-0.2mm when switching to PETG, but have never had to make such adjustments for filament differences. If someone likes to grind that 1st PLA layer down with Live-Z, I suppose they'd need to back off further for PETG. I probably keep my Live-Z on the higher end so less correction is needed.

I find final Live-Z adjustments of 0.02mm are the minimal useful amount -- no sense inputting anything lower in other words -- as I'm dialing in (slowly) to the final number. As I wrote above, I found the whole exercise of chasing per-filament Live-Z adjustments mostly a waste of time after focusing on getting Live-Z right in the first place. I'll make a tweak as I watch the 1st layer if needed, but don't find it worthwhile to try to maintain per-filament Live-Z corrections in my filament presets. I'm going to watch that 1st layer go down regardless.

YMMV and all that.

Even on my non-Prusa Sidewinder, I usually do a 7x7 grid of 15mm squares after doing manual (yech) leveling and find I can manually input corrections of +-0.02-0.06mm to close everything all the squares up nicely. Or at least until I sneeze near the thing and have to do it over again.

You think that's silly?

Heh. Just read a post about doing the nyloc bed mod to address deviations of 0.05mm. 😀 

I’m with Bobstro on this too. I hardly ever need to adjust live z. I suspect it’s because we both preheat our printing surfaces and let them normalise at close to print temperature as well as getting the pinda to a set temp before we mesh level. That makes it far far more consistent in my experience.

First layer was much more variable before I started doing that. 

RE: Filament specific Z offset

My problem is not with different brands of PETG or PLA, nor with the first layer reliability / accuracy.

I am trying to print ABS on my enclosed prusa mk3s but I am facing several difficulties finding the right settings.

One of the symptoms is the, common, bed lifting/warping ... and I read that with ABS you should put the first layer a bit more squished. Because I also print PETG quite frequently, and I have no interest in having to manually adjust the live Z parameter every time, I want to be able to save those settings in the profile of the filaments.

But I have other issues... currently around 2/3+ hours into a print, I believe that the extruder starts eating away at the plastic with the dented gears and it stops extruding... I think perhaps the enclosure temperature is causing it...

Beware ambient temps, esp. with enclosures

Posted by: @haevaristo

[...] Because I also print PETG quite frequently, and I have no interest in having to manually adjust the live Z parameter every time, I want to be able to save those settings in the profile of the filaments.

I'm not trying to preach to anyone. Definitely do what works for you. But I can say when I enthusiastically pursued this a couple of years back, I finally realized I'm going to watch that 1st layer anyways and will make a final adjustment then.

You could always create a sheet profile with the offset if it's always consistent for a type of filament.

But I have other issues... currently around 2/3+ hours into a print, I believe that the extruder starts eating away at the plastic with the dented gears and it stops extruding... I think perhaps the enclosure temperature is causing it...

If this is when printing PLA, beware ambient temps in enclosures or rooms approaching 40C as PLA can soften prematurely. More notes on diagnosing that sort of problem here.

RE: Filament specific Z offset

If this is when printing PLA, beware ambient temps in enclosures or rooms approaching 40C as PLA can soften prematurely. More notes on diagnosing that sort of problem here.

 

Nah, not PLA... ABS.

Printer works fine with PLA and PETG. Just the ABS giving me issues.

I didn't read about nyloc bed mod, and yes, I think difference of 0,02mm is academic. The thing is, Z-offsets are relative to bed mesh leveling.. and I'm quite sure SuperPINDA deviations in sensitivity are bigger than that.
I'm not arguing and I'm not necessary right on this -just sharing my opinion.

We need to put numbers to adjustments!

Posted by: @bogdanh

I didn't read about nyloc bed mod, and yes, I think difference of 0,02mm is academic. The thing is, Z-offsets are relative to bed mesh leveling.. and I'm quite sure SuperPINDA deviations in sensitivity are bigger than that.

A 0.02mm move on its own is unlikely to do much, sure. A 0.02mm on top of other adjustments is +-10% of a normal  0.2mm layer height. ALL of the measurements we use are very very small. I assume you're not routinely making adjustments of more than 0.2mm, or? Whether the actual amount is 0.02mm or the accuracy of the PINDA doesn't matter so long as the first layer is consistent. That's why I'm saying over-thinking doesn't help much. "Enough" is enough.

I'm not arguing and I'm not necessary right on this -just sharing my opinion.

Fair enough, and I'm not shouting. But if you consider that "too small", what is a "correct" amount? To repeat my earlier point, we drive a lot of new users nuts when we use ambiguous terms like "a bit" and "more". We really need to put typical numbers in examples.